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<pre><span class="sourceLineNo">001</span><a name="line.1"></a>
<span class="sourceLineNo">002</span>/*<a name="line.2"></a>
<span class="sourceLineNo">003</span> * Copyright (C) 2011 Archie L. Cobbs. All rights reserved.<a name="line.3"></a>
<span class="sourceLineNo">004</span> *<a name="line.4"></a>
<span class="sourceLineNo">005</span> * $Id: BigFatLock.html 689 2013-06-28 19:22:16Z archie.cobbs $<a name="line.5"></a>
<span class="sourceLineNo">006</span> */<a name="line.6"></a>
<span class="sourceLineNo">007</span><a name="line.7"></a>
<span class="sourceLineNo">008</span>package org.dellroad.stuff.servlet;<a name="line.8"></a>
<span class="sourceLineNo">009</span><a name="line.9"></a>
<span class="sourceLineNo">010</span>import java.io.IOException;<a name="line.10"></a>
<span class="sourceLineNo">011</span>import java.util.concurrent.Callable;<a name="line.11"></a>
<span class="sourceLineNo">012</span><a name="line.12"></a>
<span class="sourceLineNo">013</span>import javax.servlet.FilterChain;<a name="line.13"></a>
<span class="sourceLineNo">014</span>import javax.servlet.ServletException;<a name="line.14"></a>
<span class="sourceLineNo">015</span>import javax.servlet.http.HttpServletRequest;<a name="line.15"></a>
<span class="sourceLineNo">016</span>import javax.servlet.http.HttpServletResponse;<a name="line.16"></a>
<span class="sourceLineNo">017</span><a name="line.17"></a>
<span class="sourceLineNo">018</span>import org.slf4j.Logger;<a name="line.18"></a>
<span class="sourceLineNo">019</span>import org.slf4j.LoggerFactory;<a name="line.19"></a>
<span class="sourceLineNo">020</span>import org.springframework.web.filter.OncePerRequestFilter;<a name="line.20"></a>
<span class="sourceLineNo">021</span><a name="line.21"></a>
<span class="sourceLineNo">022</span>/**<a name="line.22"></a>
<span class="sourceLineNo">023</span> * Class for serializing processing using a big fat lock.<a name="line.23"></a>
<span class="sourceLineNo">024</span> *<a name="line.24"></a>
<span class="sourceLineNo">025</span> * &lt;p&gt;<a name="line.25"></a>
<span class="sourceLineNo">026</span> * The lock can be acquired using {@link #runWithLock}. This class can also be used as a servlet filter.<a name="line.26"></a>
<span class="sourceLineNo">027</span> *<a name="line.27"></a>
<span class="sourceLineNo">028</span> * &lt;p&gt;<a name="line.28"></a>
<span class="sourceLineNo">029</span> * Trace-level logging for displaying lock acquire and release events is included.<a name="line.29"></a>
<span class="sourceLineNo">030</span> */<a name="line.30"></a>
<span class="sourceLineNo">031</span>public final class BigFatLock extends OncePerRequestFilter {<a name="line.31"></a>
<span class="sourceLineNo">032</span><a name="line.32"></a>
<span class="sourceLineNo">033</span>    private static final Object BIG_FAT_LOCK = new BigFatLock();<a name="line.33"></a>
<span class="sourceLineNo">034</span>    private static final Logger LOG = LoggerFactory.getLogger(BigFatLock.class);<a name="line.34"></a>
<span class="sourceLineNo">035</span><a name="line.35"></a>
<span class="sourceLineNo">036</span>    @Override<a name="line.36"></a>
<span class="sourceLineNo">037</span>    protected void doFilterInternal(HttpServletRequest request, HttpServletResponse response,<a name="line.37"></a>
<span class="sourceLineNo">038</span>      FilterChain filterChain) throws ServletException, IOException {<a name="line.38"></a>
<span class="sourceLineNo">039</span>        if (LOG.isTraceEnabled()) {<a name="line.39"></a>
<span class="sourceLineNo">040</span>            LOG.trace("thread " + Thread.currentThread() + " waiting for " + BIG_FAT_LOCK);<a name="line.40"></a>
<span class="sourceLineNo">041</span>            synchronized (BIG_FAT_LOCK) {<a name="line.41"></a>
<span class="sourceLineNo">042</span>                LOG.trace("thread " + Thread.currentThread() + " acquired " + BIG_FAT_LOCK);<a name="line.42"></a>
<span class="sourceLineNo">043</span>                try {<a name="line.43"></a>
<span class="sourceLineNo">044</span>                    filterChain.doFilter(request, response);<a name="line.44"></a>
<span class="sourceLineNo">045</span>                } finally {<a name="line.45"></a>
<span class="sourceLineNo">046</span>                    LOG.trace("thread " + Thread.currentThread() + " releasing " + BIG_FAT_LOCK);<a name="line.46"></a>
<span class="sourceLineNo">047</span>                }<a name="line.47"></a>
<span class="sourceLineNo">048</span>            }<a name="line.48"></a>
<span class="sourceLineNo">049</span>        } else {<a name="line.49"></a>
<span class="sourceLineNo">050</span>            synchronized (BIG_FAT_LOCK) {<a name="line.50"></a>
<span class="sourceLineNo">051</span>                filterChain.doFilter(request, response);<a name="line.51"></a>
<span class="sourceLineNo">052</span>            }<a name="line.52"></a>
<span class="sourceLineNo">053</span>        }<a name="line.53"></a>
<span class="sourceLineNo">054</span>    }<a name="line.54"></a>
<span class="sourceLineNo">055</span><a name="line.55"></a>
<span class="sourceLineNo">056</span>    /**<a name="line.56"></a>
<span class="sourceLineNo">057</span>     * Invoke the given action after acquiring the big fat lock.<a name="line.57"></a>
<span class="sourceLineNo">058</span>     */<a name="line.58"></a>
<span class="sourceLineNo">059</span>    public static void runWithLock(Runnable action) {<a name="line.59"></a>
<span class="sourceLineNo">060</span>        if (LOG.isTraceEnabled()) {<a name="line.60"></a>
<span class="sourceLineNo">061</span>            LOG.trace("thread " + Thread.currentThread() + " waiting for " + BIG_FAT_LOCK);<a name="line.61"></a>
<span class="sourceLineNo">062</span>            synchronized (BIG_FAT_LOCK) {<a name="line.62"></a>
<span class="sourceLineNo">063</span>                LOG.trace("thread " + Thread.currentThread() + " acquired " + BIG_FAT_LOCK);<a name="line.63"></a>
<span class="sourceLineNo">064</span>                try {<a name="line.64"></a>
<span class="sourceLineNo">065</span>                    action.run();<a name="line.65"></a>
<span class="sourceLineNo">066</span>                } finally {<a name="line.66"></a>
<span class="sourceLineNo">067</span>                    LOG.trace("thread " + Thread.currentThread() + " releasing " + BIG_FAT_LOCK);<a name="line.67"></a>
<span class="sourceLineNo">068</span>                }<a name="line.68"></a>
<span class="sourceLineNo">069</span>            }<a name="line.69"></a>
<span class="sourceLineNo">070</span>        } else {<a name="line.70"></a>
<span class="sourceLineNo">071</span>            synchronized (BIG_FAT_LOCK) {<a name="line.71"></a>
<span class="sourceLineNo">072</span>                action.run();<a name="line.72"></a>
<span class="sourceLineNo">073</span>            }<a name="line.73"></a>
<span class="sourceLineNo">074</span>        }<a name="line.74"></a>
<span class="sourceLineNo">075</span>    }<a name="line.75"></a>
<span class="sourceLineNo">076</span><a name="line.76"></a>
<span class="sourceLineNo">077</span>    /**<a name="line.77"></a>
<span class="sourceLineNo">078</span>     * Invoke the given action after acquiring the big fat lock.<a name="line.78"></a>
<span class="sourceLineNo">079</span>     */<a name="line.79"></a>
<span class="sourceLineNo">080</span>    public static &lt;V&gt; V runWithLock(Callable&lt;V&gt; action) throws Exception {<a name="line.80"></a>
<span class="sourceLineNo">081</span>        if (LOG.isTraceEnabled()) {<a name="line.81"></a>
<span class="sourceLineNo">082</span>            LOG.trace("thread " + Thread.currentThread() + " waiting for " + BIG_FAT_LOCK);<a name="line.82"></a>
<span class="sourceLineNo">083</span>            synchronized (BIG_FAT_LOCK) {<a name="line.83"></a>
<span class="sourceLineNo">084</span>                LOG.trace("thread " + Thread.currentThread() + " acquired " + BIG_FAT_LOCK);<a name="line.84"></a>
<span class="sourceLineNo">085</span>                try {<a name="line.85"></a>
<span class="sourceLineNo">086</span>                    return action.call();<a name="line.86"></a>
<span class="sourceLineNo">087</span>                } finally {<a name="line.87"></a>
<span class="sourceLineNo">088</span>                    LOG.trace("thread " + Thread.currentThread() + " releasing " + BIG_FAT_LOCK);<a name="line.88"></a>
<span class="sourceLineNo">089</span>                }<a name="line.89"></a>
<span class="sourceLineNo">090</span>            }<a name="line.90"></a>
<span class="sourceLineNo">091</span>        } else {<a name="line.91"></a>
<span class="sourceLineNo">092</span>            synchronized (BIG_FAT_LOCK) {<a name="line.92"></a>
<span class="sourceLineNo">093</span>                return action.call();<a name="line.93"></a>
<span class="sourceLineNo">094</span>            }<a name="line.94"></a>
<span class="sourceLineNo">095</span>        }<a name="line.95"></a>
<span class="sourceLineNo">096</span>    }<a name="line.96"></a>
<span class="sourceLineNo">097</span><a name="line.97"></a>
<span class="sourceLineNo">098</span>    /**<a name="line.98"></a>
<span class="sourceLineNo">099</span>     * Verify that the current thread is holding the big fat lock.<a name="line.99"></a>
<span class="sourceLineNo">100</span>     */<a name="line.100"></a>
<span class="sourceLineNo">101</span>    public static boolean isLockHeld() {<a name="line.101"></a>
<span class="sourceLineNo">102</span>        return Thread.holdsLock(BIG_FAT_LOCK);<a name="line.102"></a>
<span class="sourceLineNo">103</span>    }<a name="line.103"></a>
<span class="sourceLineNo">104</span><a name="line.104"></a>
<span class="sourceLineNo">105</span>    @Override<a name="line.105"></a>
<span class="sourceLineNo">106</span>    public String toString() {<a name="line.106"></a>
<span class="sourceLineNo">107</span>        return "BigFatLock@" + System.identityHashCode(this);<a name="line.107"></a>
<span class="sourceLineNo">108</span>    }<a name="line.108"></a>
<span class="sourceLineNo">109</span>}<a name="line.109"></a>
<span class="sourceLineNo">110</span><a name="line.110"></a>




























































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